1. Field of the Invention
The invention generally relates to medical devices and procedures where fluids preferably are simultaneously infused and aspirated from the patient. The invention more particularly concerns a multi-use, or preferably a single-use pumping system, to infuse and aspirate liquids to and from a surgical site through a catheter, conduit or tube.
2. Description of Related Art
The use of pumping mechanisms to flush debris created during diagnostic and therapeutic procedures is not new, see for example U.S. Pat. No. 6,258,061 (Drasler), and U.S. Pat. No. 5,879,361 (Nash). These inventions describe using a catheter for clearing an occluded blood vessel, by using either a rotating impact head, coupled with a flushing mechanism (Nash) or using high pressure jets of fluid to clear the thrombus (Drasler).
Nash discloses the use of peristaltic pumps as the infusion and extraction pumps (Nash). Peristaltic pumps have a number of attributes that account for their widespread use in medical applications. The pumps are accurate in metering flow over a range of pressures. The maximum and minimum variations in flow rate during a pump cycle do not vary too greatly from the mean flow rate. The fluid pathway (e.g., a tube) of the pumps is easily sterilized and visible. When not in operation, there is very little if any leakage through the peristaltic pump head.
On the other hand, peristaltic pumps are relatively energy inefficient, thereby requiring AC power or large batteries as their power supply. In fact, the pumping system that uses such pumps is usually sufficiently large that it will not fit within the confines of the “sterile field” of the operating room. Thus, such a pump system typically is located at a remote region of the operating room, distant from the doctor, who must then direct another person to actually operate, or at least monitor, the pump system.
Drasler discloses the use of jets to emulsify the thrombus in the blood vessel. The high pressure jets as described are generated “with a positive displacement pump, such as a piston pump . . . ” which is designed to be disposable for sanitary reasons (Drasler). The pump can operate under pulsatile or steady flow. The invention described by Drasler may allow the fluid to exhaust by directing the spray of the catheter inlet back towards the exhaust outlet of the catheter, or alternatively “a vacuum pump to provide for removal of the fragmented thrombus or tissue, or a roller pump may be used to accomplish a similar effect.”
The Drasler inventions pertain to high pressure applications, such as cutting and emulsifying thrombi using liquid jets. When the medical intervention pertains to other treatments such as infusion of a diagnostic agent or a therapy, however, such single cylinder reciprocating pumps, by their design, result in large variations in instantaneous flow rate during a pump cycle. The fluctuations in the instantaneous flow rate range from a minimum flow rate of zero to a maximum that is a number of times greater than the mean flow rate. The fluctuating flow rate has a pronounced impact on the pressure in the aspiration.
The variations in instantaneous flow rate as a result of the back and forth motion of the pump piston require the liquid in the conduit connecting the patient to the pump to be accelerated during increasing flow, and decelerated during decreasing flow. When aspirating fluids, the force required to accelerate the flow in the conduit results in a decreased pressure at the entrance to the pump. The variations in flow rate also increase the instantaneous frictional losses in the catheter because the frictional losses are related to the square of the flow's velocity. The frictional losses at peak instantaneous flows are substantially higher than the losses associated with a steady flow at the mean flow rate. The force required to overcome the increased losses also results in a lower pressure at the pump entrance.
Both of the above effects are particularly troublesome in aspiration pumps since the minimum pressure at the pump is limited to the liquid's vapor pressure. If pressure falls to the liquid's vapor pressure, cavitation will occur (as the liquid boils) and aspiration will be impeded. Specifically, the evolving of vapor will render the actual extraction rate of liquid indeterminate. Further, if the system were to be shut off at that point, it is at least theoretically possible for an air bubble to be pushed back up the catheter into the patient, for example, if the aspiration pathway flow is reversed due to the introduction of drugs or contrast media, via activation of an injection port on a guide connector branch.
Another drawback associated with the reciprocating pump is leakage through the pump when it is stopped. The leakage occurs in the direction of flow and is due to the arrangement of the check-valves within the pump, which allow virtually unrestricted flow only in the intended direction. This drawback becomes problematic when the aspiration conduit is located in an elevated pressure environment such as an artery or the aspiration conduit is used as a pathway to introduce medication or other liquids when aspiration is stopped. Specifically, the arterial blood pressure can be sufficient to cause bleeding through the aspiration conduit, through the aspiration pump and into the aspiration or extraction bag.
The present invention addresses and solves these and other shortcomings of the prior art.